This invention relates to the selective control of a detonator, or a group of detonators, in a blasting system which includes a plurality of the detonators.
One blasting system employs so-called “smart keys” which contain an embedded group identifier that is unique to a given matched set of keys. The key group identifier accompanies blasting messages in the system and is validated to ensure that the keys, in use in the system, have matching identifiers before allowing blasting. The system also allows a subset of blasting machines, which should participate in a blast, to be selected. This is done by means of commands directed to each blasting machine to enable the participation of that machine in subsequent blasting activities.
U.S. Pat. No. 8,385,042 discloses a method of communicating with a subgroup of wireless detonators that involves sending a group identifier in a message to the wireless detonators. Each detonator must then verify that the transmitted group identifier matches an identifier which is internally stored in the detonator. A similar technique is described in US2011/0174181 wherein a transmitter identifier code most match a receiver code in order for a detonator to be initiated.
U.S. Pat. No. 7,848,078 discloses a method of communicating with detonators in which a roll call signal includes coding to ensure that the signal is acted on only by a specific detonator assembly or by a specific group of detonator assemblies. This is done by using different frequencies for the signal.
WO2012/061850 describes a technique wherein a fire command is specifically chosen, or randomly generated, as required. This approach enables groupings of detonators to be achieved by choosing different fire commands for different groups of detonators. However, other broadcast commands are not identified as belonging to a specific group.
US2012/353203 presents a system wherein a safety data structure, communicated to a blasting machine, contains a system identifier and a device-identifier. This technique can be used to achieve selective control of groups of detonators.
In a wireless detonator system, based on the use of wireless detonator assemblies, communications are often accomplished by signals which are transmitted by modulating a magnetic field. Operating frequencies are low to ensure effective signal propagation through the earth. Consequently, data transfer rates are also low. A receiver circuit at a detonator assembly can be tuned to a specific-frequency by means of a high-Q receiver but this technique makes use of separate frequencies, to accomplish group-specific control, impractical if an additional group identifier accompanies each message then communications would be slower than is desirable.
An object of the invention is to provide a method of controlling a selected detonator assembly, or a selected group of detonators assemblies, which does not require a group identifier to be transmitted with each group-specific command, and which does not require the use of separate frequencies. This allows the communication overhead to be reduced.